Development of a new method with the aim of analysing N-nitrosamines in workplace air within the scope of occupational safety - NNOccSafe

Status:

completed 07/2025

Aims:

Aim of the research project was to create an alternative analysis method for nitrosamines with improved sensitivity and reduced workload compared to the current state of the art, which is a combination of gas chromatography and a thermal energy analyser (GC-TEA). The new method was to be based on the combination of gas chromatography and ion mobility spectrometry (GC-IMS) and coupled with a highly concentrating and automatable sample preparation and injection technique. Additionally, in this context, the GC-IMS system promised high robustness and, due to comparatively low acquisition and operating costs, improved economic aspects.

Activities/Methods:

Two methods were developed as part of the research project: one for analysing nitrosamines in drinking water and the other for analysing nitrosamines in the air at the workplace. To this end, the techniques of solid-phase microextraction (SPME, SPME Arrow), large-volume injection (LVI), in-tube extraction (ITEX, a form of dynamic headspace), static headspace, solid-phase extraction (SPE) and thermal desorption (TD) in combination with GC-IMS were evaluated, compared and combined in order to achieve the strongest enrichment of the analytes in each case. For the water analysis of nitrosamines, this resulted in a method combining two enrichment strategies using SPE and ITEX (SPE-ITEX-GC-IMS) for water analysis, and for air analysis, a TD-based sampling and injection method coupled with the GC-IMS system (TD-GC-IMS) was used. Extensive optimisation and validation measurements were carried out for both methods so that they could ultimately be applied to real matrices and compared with the respective state of the art.

Results:

The first results were achieved in the area of calibration gas generation: the permeation behaviour of nine nitrosamines was investigated using a calibration gas generator and calibration gases in the concentration range were produced. These calibration gases were then used to carry out various measurement series as part of method development and optimisation.

Various validation parameters were tested for the TD-GC-IMS method developed. Under various storage conditions, a stability of 10 days was confirmed using stainless steel sample cartridges with Swagelok sealing caps. With quantification limits for the nine nitrosamines, the sensitivity was slightly lower than that of the GC-TEA technique, but within the range of the currently applicable tolerance and acceptance values. With a low concentration of nitrosatable precursor substances, the use of a test gas facility set up for this series of measurements confirmed that even at high nitrogen oxide concentrations (exceeding the occupational exposure limit by a factor of 2), no artificial nitrosamine formation occurred on the sampler. When analysing real air samples in an underground landfill site, only the nitrosamine NDMA could be reliably detected on the sample carriers. The concentration determined was in the range for the measurement location with low dust pollution, which corresponds well with the results of the parallel GC-TEA measurement.

The measurement parameters of the SPE-ITEX-GX-IMS method were strategically optimised according to a statistical experimental design and then applied to various drinking waters. Detection limits for the nine nitrosamines in this matrix ranged between 1 and 22 ng/L. Although this meets the drinking water purity requirements of some countries in Europe and North America, it exceeds the detection limits achieved by mass spectrometry by a factor of 100. The analysis of the drinking water revealed no contamination with nitrosamines.

While relevant findings on the sampling and analysis of nitrosamines were gained in the project and the foundation was laid for research into alternative techniques to the GC-TEA method, the methods developed cannot be used without further extensive optimisation and refinement.

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